CAIRO — Al-Qaida on Friday vowed avenge the killing of Osama bin Laden with more attacks on the West, saying that Americans' "happiness will turn to sadness."

The Internet statement, the first by the terror network since its leader was slain in a U.S. commando raid against his Pakistani hideout, was apparently designed to convince followers that it will remain vigorous and intact even after its founder's demise.

"The blood of the holy warrior sheik, Osama bin Laden, God bless him, is too precious to us and to all Muslims to go in vain," the statement said. "We will remain, God willing, a curse chasing the Americans and their agents, following them outside and inside their countries."

"Soon, God willing, their happiness will turn to sadness," it said, "their blood will be mingled with their tears."

A Western intelligence official said no concrete threat has emerged so far that authorities considered credible. "There have been mentions of shootings, bombings and random violence, though it is not surprising, given bin Laden's death," the official said, speaking on condition of anonymity.

Authorities in the U.S. and Europe chose not to elevate threat levels.

Interpol has asked law enforcement agencies in 188 countries to be on alert for retaliatory attacks. Communities have been warned to report anything suspicious. Embassies and some American businesses have added new security measures.

The al-Qaida statement, titled "You lived as a good man, you died as a martyr," did not name a successor to bin Laden. His deputy, Ayman al-Zawahri, is now the most prominent figure in the group and a likely contender to take his place.

Although the statement's authenticity could not be independently confirmed, it was considered to be authentic. It was posted on militant websites Friday by the al-Fajr Center, al-Qaida's online media distribution network, and the writing style was typical for al-Qaida. The statement was issued in the name of the organization's General Command and dated Tuesday, the day after bin Laden's death.

White House press secretary Jay Carney said U.S. officials are aware of the statement and the threat. "What it does obviously is acknowledge the obvious, which is that Osama bin Laden was killed," said Carney. "We're quite aware of the potential for (terrorist) activity and are highly vigilant on that matter for that reason."

Despite the new threats against the United States, the overall theme of the al-Qaida statement was that of continuity for the organization. Much of the 11-paragraph statement was dedicated to underlining that al-Qaida would live on, depicting him as another in a line of "martyrs" from the group.

"Sheik Osama didn't build an organization to die when he dies," the statement read. "The university of faith, Quran and jihad from which bin Laden graduated will not close its doors," it added.

"The soldiers of Islam will continue in groups and united, plotting and planning without getting bored, tired, with determination, without giving up until striking a blow," the statement said.

It said bin Laden was killed "along an established path followed by the best of those who came before him and those who will come after him."

The acknowledgment by al-Qaida should remove doubt among all but the most die-hard conspiracy theorists that bin Laden is in fact dead.

The need to provide proof was behind some arguments that the U.S. should release a photo of the slain terror leader. President Barack Obama has chosen to withhold the photo.

Earlier Friday, hundreds of members of radical Islamic parties protested in several Pakistan cities against the U.S. raid. Many chanted "Osama is alive" and criticized the U.S. for violating the country's sovereignty.

In the statement, al-Qaida also called on Pakistanis to revolt against the country's leaders to "cleanse the shame." And it said that an audio message bin Laden recorded a week before his death would be issued soon.

The writers of the al-Qaida statement appeared unaware of the U.S. announcement that bin Laden's body had been buried at sea. The statement warned against mishandling or mistreating bin Laden's body and demanded that it be handed over to his family, saying "any harm (to the body) will open more doors of evil, and there will be no one to blame but yourselves."

There had been hope that bin Laden's death would cause the Afghan Taliban to rethink its ties with al-Qaida — a union the U.S. insists must end if the insurgents want to talk peace. The foundation of their relationship was believed to be rooted in bin Laden's long friendship with the Taliban's reclusive leader, Mullah Mohammed Omar.

But on Friday, the Afghan Taliban issued a statement saying bin Laden's death will only boost morale among insurgents fighting the U.S. and NATO.

The Taliban praised bin Laden for his sacrifice in the Afghan war against the Soviets in the 1980s and said anyone who believes his death will undermine the current conflict is displaying a "lack of insight."

Al-Zawahri, an Egyptian who is the most likely successor to bin Laden, is a less charismatic, unifying figure. He is believed to lack bin Laden's ability to bring together the many nationalities and ethnic groups that make up al-Qaida. His appointment could further fracture an organization that is thought to be increasingly decentralized.

Al-Zawahri has long been considered the operational head of al-Qaida while bin Laden was assumed to be an inspirational figure who was uninvolved in operations.

But documents Navy SEALs seized in Monday's raid on the hideout in the Pakistani town of Abbottabad suggest that bin Laden may have been more involved in operations than had been thought.

The documents reveal plans for derailing an American train on the 10th anniversary of the Sept. 11, 2011 attacks. Counterterrorism officials said they believe the plot was in the initial planning stages at the time.

Al-Qaida, which carried out the attacks on the World Trade Center and the Pentagon, has never abandoned its hope of again attacking the U.S. homeland.

U.S. Sen. Susan Collins, a Republican from Maine, urged that the country's threat level be stepped up while the material seized from bin Laden's compound is reviewed.

In Europe, security officials said there is no specific plot to justify raising the threat level.

British cleric Anjem Choudary, who helped organize Friday's demonstration outside the U.S. Embassy in London, said revenge attacks in Britain and abroad were likely. Choudary used to head the outlawed al-Muhajiroun group and is now a member of the Muslims Against Crusades group.

"I think Britain is more likely to face a 7/7 today than ever," he said in reference to the London suicide bombings on July 7, 2005. "Osama bin Laden was a high-profile leader. If the Americans talk of justice, they shouldn't have killed him. The next attacks will likely be high profile and could very well happen in Europe or in the U.S."

Meanwhile, Obama thanked the U.S. commandos he sent after bin Laden, saluting them Friday on behalf of America and people all over the world. "Job well done," he declared.

The president spoke to a hangar full of cheering soldiers after meeting privately with the full assault team — Army helicopter pilots and Navy SEAL commandos — who executed the raid early Monday.

"Thanks to the incredible skill and courage of countless individuals — intelligence, military over many years — the terrorist leader that struck our nation 9/11 will never threaten America again," Obama said.

Intelligence analysts are examining a notebook taken from bin Laden's house to see if contains his handwriting, officials told NBC News. The notebook had an entry dated February 2010 about attacking U.S. trains.

The train-attack scenario came out quickly because they were in paper documents. The bulk of the material taken from the house is in digital form, much of it encrypted, which will require more time to unscramble and read, the official said.

Asked if the material contains valuable leads about the whereabouts of top al-Qaida figures, another official said, "It contains leads, but we don't know yet how valuable they are."

Senior U.S. officials also told NBC News that some of the digital material also included videos of life in the compound and unreleased propaganda.

The wealth of information pulled from the compound has reinforced the belief that bin Laden played a strong role in planning and directing attacks by al-Qaida and its affiliates in Yemen and Somalia, senior U.S. officials told The Associated Press.

And the data further demonstrates to the U.S. that top al-Qaida commanders and other key insurgents are scattered throughout Pakistan, not just in the rugged border areas, and are being supported and given sanctuary by Pakistanis, a senior defense official said.

Pakistan under pressure
Anger and suspicion between Washington and Islamabad over the raid in Abbottabad showed no sign of abating.

A U.S. drone killed 17 suspected militants in northwest Pakistan, despite warnings from the Pakistani military against the mounting of attacks within its borders.

About 1,500 Islamists rallied in the southwestern city of Quetta to vow revenge for bin Laden's death and there were small protests elsewhere. Afghan Taliban and Islamist Indonesian youths made similar threats.

One of bin Laden's wives told Pakistani interrogators the al Qaeda leader had been living for five years in the compound where he was killed, a Pakistani security official told Reuters.

The disclosure appeared sure to heighten U.S. suspicions that Pakistani authorities had been either grossly incompetent or playing a double game in the hunt for bin Laden and the two countries' supposed partnership against violent Islamists.

Pakistani security forces took 15 or 16 people into custody from the Abbottabad compound after U.S. forces removed bin Laden's body, said the security official. They included bin Laden's three wives and several children.

Video: Al-Qaida confirms bin Laden death, vows reprisal

>>>good evening. today, the
president of the united states
delivered the thanks of a grateful nation to a group of men whose names we can't know and whose faces we can't show. members of the
u.s. navy
s.e.a.l. team who pulled off the high-stakes raid that killed
osama bin laden
. the president went to ft. campbell, kentucky, where
halfway around the world
, we're still learning more about the raid, what was grabbed, the official confirmation of
bin laden
's death, and a potential threat to all of us once again. we start off with two reports tonight, beginning at the scene,
ann curry
on the ground in pakistan tonight. ann, good evening.

>> reporter: brian, good evening to you. and confirming
osama bin laden
's death today,
al qaeda
is clearly trying to reinvigorate its jihad and sent a message that its war on americans will go on without him. at the same time,
u.s. intelligence
officials tell
nbc
news
bin laden
was fully engaged in
al qaeda
operations a s at the time of his death. coordinated protested that announced the raid against the killing of
osama bin laden
in multipl cities today as
al qaeda
reacted for the first time. quote, soon, with god's help, we shall flip their celebrations into sorrow and their blood shall mix with tears.

>>soon could mean anything from the next three days the next three years. it's difficult to know and it's important to emphasize
al qaeda
uses its language whether or not it has an attack in score.

>>these images are the newest from inside the compound where they tell
nbc
news
bin laden
was far from retired and was
al qaeda
's operational leader.
u.s. intelligence
also tells
nbc
news, a lot of video as well as details of plots around the world and associates were found.
osama bin laden
's compound is just beyond these buildings, but today, the pakistani soldiers have told us all the media has to be pushed back and if they even see our cameras, they threaten to take them. local officials in abbottabad said the compound is now cleansed. they have as many as three of
bin laden
's wives in custody under interrogation. the cia asked for access to the wives, especially
bin laden
's last and favorite wife. she was known to be devoted to
bin laden
and was in the room when he died and she told interrogators that bein laden and his family have been living in the abbottabad combound for the last five years.
al qaeda
also said today it will soon release a voice recording of
bin laden
which it claims was made a week before his death.

An aerial view shows the residential area of Abbottabad, Pakistan, where Osama bin Laden was found and killed by U.S. commandos.
(Asif Hassan / AFP - Getty Images)
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A general view of the town of Abbottabad, May 6. Bin Laden was living in a large house close to a military academy in this garrison town, a two-and-a-half hour-drive from the capital, Islamabad.
(Khaqan Khawer / EPA)
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Supporters of Pakistani religious party Jamaat-e-Islami rally to condemn the killing of bin Laden, in Abbottabad on May 6.
(Aqeel Ahmed / AP)
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A Pakistani woman photographs her daughter on May , at a gate of the compound where bin Laden was caught and killed.
(Aqeel Ahmed / AP)
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School girls pass by armed Pakistani policemen guarding the sealed entrance to the compound in Abbottabad, May 5, in which bin Laden had been living.
(MD Nadeem / EPA)
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A Pakistani police officer gestures at a checkpoint along a road leading to a house where bin Laden was captured and killed in Abbottabad. Area residents were still confused and suspicious about bin Laden's death, which took place before dawn on Monday.
(Anjum Naveed / AP)
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Part of a damaged U.S. MH-60 helicopter lies the compound. The helicopter was destroyed by U.S. forces after a mechanical failure left it unable to take off.
(Reuters)
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A still image from video obtained by ABC News shows blood stains in the interior of the house where bin Laden was killed.
(ABC News via Reuters)
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Aerial views released by the Department of Defense show the area in Abbottabad in 2004, left, before the house was built, and in 2011, right.
(Department of Defense via Reuters)
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Boys collect pieces of metal from a wheat field outside bin Laden's house, seen in the background, on May 3. People showed off small parts of what appeared to be a U.S. helicopter that the U.S. says malfunctioned and was blown up by the American team as it retreated.
(Anjum Naveed / AP)
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An image from video seized from the walled compound of al-Qaida leader Osama bin Laden in Abbottabad, and released by the U.S. Department of Defense, shows Osama bin Laden watching TV. He is said to have spent his last weeks in a house divided, amid wives riven by suspicions. On the top floor, sharing his bedroom, was his youngest wife and favorite. The trouble came when his eldest wife showed up and moved into the bedroom on the floor below.
(Department of Defense via AP)
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Editor's note:
This image contains graphic content that some viewers may find disturbing.